objtool, kcsan: Remove memory barrier instrumentation from noinstr

Teach objtool to turn instrumentation required for memory barrier
modeling into nops in noinstr text.

The __tsan_func_entry/exit calls are still emitted by compilers even
with the __no_sanitize_thread attribute. The memory barrier
instrumentation will be inserted explicitly (without compiler help), and
thus needs to also explicitly be removed.

Signed-off-by: Marco Elver <elver@google.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 31 insertions, 6 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 61dfb66b30b6..a9a1f7259d62 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1072,11 +1072,11 @@ static void annotate_call_site(struct objtool_file *file,
 	}
 
 	/*
-	 * Many compilers cannot disable KCOV with a function attribute
-	 * so they need a little help, NOP out any KCOV calls from noinstr
-	 * text.
+	 * Many compilers cannot disable KCOV or sanitizer calls with a function
+	 * attribute so they need a little help, NOP out any such calls from
+	 * noinstr text.
 	 */
-	if (insn->sec->noinstr && sym->kcov) {
+	if (insn->sec->noinstr && sym->profiling_func) {
 		if (reloc) {
 			reloc->type = R_NONE;
 			elf_write_reloc(file->elf, reloc);
@@ -1991,6 +1991,31 @@ static int read_intra_function_calls(struct objtool_file *file)
 	return 0;
 }
 
+/*
+ * Return true if name matches an instrumentation function, where calls to that
+ * function from noinstr code can safely be removed, but compilers won't do so.
+ */
+static bool is_profiling_func(const char *name)
+{
+	/*
+	 * Many compilers cannot disable KCOV with a function attribute.
+	 */
+	if (!strncmp(name, "__sanitizer_cov_", 16))
+		return true;
+
+	/*
+	 * Some compilers currently do not remove __tsan_func_entry/exit nor
+	 * __tsan_atomic_signal_fence (used for barrier instrumentation) with
+	 * the __no_sanitize_thread attribute, remove them. Once the kernel's
+	 * minimum Clang version is 14.0, this can be removed.
+	 */
+	if (!strncmp(name, "__tsan_func_", 12) ||
+	    !strcmp(name, "__tsan_atomic_signal_fence"))
+		return true;
+
+	return false;
+}
+
 static int classify_symbols(struct objtool_file *file)
 {
 	struct section *sec;
@@ -2011,8 +2036,8 @@ static int classify_symbols(struct objtool_file *file)
 			if (!strcmp(func->name, "__fentry__"))
 				func->fentry = true;
 
-			if (!strncmp(func->name, "__sanitizer_cov_", 16))
-				func->kcov = true;
+			if (is_profiling_func(func->name))
+				func->profiling_func = true;
 		}
 	}